The use of power take-off (PTO) devices to provide power to accessories on vehicles such as trucks is a well-known technology. When using a PTO device to power an accessory, it is desirable to use automated speed controllers to control the amount of power produced by a power plant such as an engine. Currently, many engine speed controllers for use while a PTO device is active use a proportional-integral-derivative (PID) control technique to establish and hold engine speed set points. In a PID control technique for managing engine speed, an error value is determined as a difference between a target engine speed value and an actual engine speed value. The PID control technique determines a corrected torque demand by determining a proportional term value (related to the current value of the error), an integral term value (related to past values of the error), and a derivative term value (related to the rate of change of values of the error), multiplying each of these values by respective gain values, and adding the resulting products. Behavior of the PID control technique may be changed by altering the proportional gain value, the integral gain value, and the derivative gain value.
There are a wide variety of accessories that may be powered by a PTO device, many of which have different engine speed, load, and response requirements/characteristics. Typically, the control characteristics of the PID control technique are fixed for a given vehicle model or engine model. For vehicle and engine models that can have multiple configurations with different accessories, fixed control characteristics make meeting the customer demands and/or accessory operating requirements difficult. For example, one instance of a given vehicle model may be equipped with a fluid pump (such as a pump for delivering gasoline or milk, a water pump for a fire truck, and/or the like) that draws a relatively small, stable amount of power from the engine via the PTO device. Another instance of the given vehicle model may be equipped with a vacuum accessory that draws a variable amount of power from the engine via the PTO device, wherein the amount may vary randomly and by large amounts (such as when a nozzle of the vacuum is momentarily blocked, causing the power demand to spike until the nozzle is unblocked).
Some previous techniques have tried to mitigate this problem by offering two standard sets of control characteristics for PID control techniques: slow response and fast response. Upon installation of an accessory on the vehicle, predetermined gain settings that provide either slow response (e.g., a smaller proportional gain, little or zero derivative gain) or fast response (e.g., a larger proportional gain, a higher derivative gain) may be programmed into a PID controller. However, a number of applications still may not get the engine speed stability and/or response they desire, particularly if their requirements fall between the behavior provided by the predetermined slow response and fast response settings. Further, when predetermined gain settings are specified using existing techniques, changing the control characteristics from one set of predetermined gain settings to another set of predetermined gain settings typically uses OEM specific tools to install a new calibration file.
In some previous systems, technicians are allowed to directly modify the gain settings during maintenance to suit a vehicle operator's needs. While this option allows for adjustability, it often causes more trouble due to the technician's lack of familiarity with PID control techniques and lack of definitive application-specific guidance on how to adjust the gain values to obtain the desired control characteristics. The vehicle operator may be left confused, frustrated, and with a non-functioning or poorly performing PTO device.